Former White House chief of staff Reince Priebus on Monday picked a candidate in the Republican primary for U.S. Senate taking place in his home state of Wisconsin and called her opponent’s candidacy “a scam.”

Priebus endorsed state Sen. Leah Vukmir, who is running against first-time candidate Kevin Nicholson, 39, a former U.S. Marine, for the Republican nomination to face Democrat Tammy Baldwin.

Vukmir is “a proven leader who will stand with President Trump,” Priebus said.

Priebus has not endorsed any other candidates so far in this election cycle, but he and Vukmir have known each other a long time. He grew up in Wisconsin and rose through the state party to become chairman in 2007.

Priebus, who was chairman of the Republican National Committee from 2011 to 2016, is now a leading figure in the state’s Republican establishment, which includes House Speaker Paul Ryan, Gov. Scott Walker and Sen. Ron Johnson.

While Priebus doesn’t speak for any of the other figures, his backing is an early signal that the Wisconsin GOP is behind Vukmir in the August primary.

Nicholson’s spokesman, Brandon Moody, responded to news of Priebus’s endorsement by email: “As a former combat Marine with tours in Iraq and Afghanistan, Kevin has shown exactly the type of patriotism and volunteerism that is so important to the defense of our nation and our way of life.”

In a phone interview Monday, Priebus said Nicholson is unproved and should have done more to build relationships and support inside the Wisconsin GOP before running for office. Priebus focused on Nicholson’s role as president of the College Democrats of America when he was an undergraduate at the University of Minnesota.

“I was a president of the the college Republicans — I know what type of people these are,” Priebus said. “These are dyed in the wool, hard-core, excited party people, which is great. But it might be wise if you want to run for the U.S. senate, maybe you ought to do a few things along the way to prove that this conversion is actually real. That’s all.

“To come from [being] the former president of the College Democrats — that to me is even more outlandish, that he is going to give the Republican Party a lesson as far as what’s conservative and what isn’t,” Priebus said. “It’s a bunch of crap to me.

“It’s not too much to ask to say, ‘Maybe I could raise a few dollars for the party, or maybe I could work a few years for Ron Johnson or Scott Walker,’” Priebus said. “But he’s done nothing. It seems like a scam to me.”

“Reince must have hit his head pretty hard when Trump kicked him to the curb,” Moody retorted.

Priebus disputed charges that Vukmir, 59, is not conservative enough.

“The idea that Leah is being labeled as establishment I find to be complete insanity, because she was the one that was constantly pushing the envelope against leadership to make things a little more conservative and at times even pushing against Gov. Walker when it came to many of these reforms that people are excited about in Wisconsin,” Priebus said.

For example, he said, Vukmir threatened to support a primary challenge to a fellow Republican state senator if he did not support her school choice bill in 2005, and he backed down. More recently, she told the Senate majority leader she would block the 2016 and 2017 state budget if a measure to repeal the prevailing wage — a minimum salary requirement on state construction projects — was not included.

“I have watched conservative people get pushed around by this phony mantra about antiestablishment that I find it so dishonest that I can’t sit here and not say anything,” Priebus said.